Automotive relay question

D

DaveC

Guest
I have a 12V SPST cube relay in my junque box. The diagram molded into the
relayšs housing includes a component connected in parallel with the coil
which looks suspiciously like a resistor.

Itšs not a back-emf diode: I connected the relay coil using both polarities
(using a current-limited power supply) and the same current draw is measured.


What is the purpose of this resistor?

Thanks,
Dave
 
Followups set to sci.electronics.components .

In sci.electronics.components DaveC <invalid@invalid.net> wrote:
I have a 12V SPST cube relay in my junque box. The diagram molded into
the relay's housing includes a component connected in parallel with
the coil which looks suspiciously like a resistor. [...]

What is the purpose of this resistor?
Click to expand...

It suppresses the inductive spike when the relay turns off. See page
3 of the Tyco application note
http://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=Automotive_Relay_Applications&DocType=CS&DocLang=EN
or
<http://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=Automotive_Relay_Applications&DocType=CS&DocLang=EN>
or even
http://is.gd/uGsYcA

I knew you could get automotive relays with nothing, a diode, or a
resistor across the coil, but I'd never heard before that any of these
shorten the life of the relay. I wonder what the mechanism is... does
it damage the coil winding insulation, or does it try to move the
armature a little, or what?

Matt Roberds
 
In article <0001HW.D066606206DB1E51B05399BF@news.eternal-september.org>,
invalid@invalid.net says...
I have a 12V SPST cube relay in my junque box. The diagram molded into the
relayšs housing includes a component connected in parallel with the coil
which looks suspiciously like a resistor.

Itšs not a back-emf diode: I connected the relay coil using both polarities
(using a current-limited power supply) and the same current draw is measured.


What is the purpose of this resistor?

Thanks,
Dave
Click to expand...

more than likely a snubber network, they normally have a
resistor and cap in a single component..

Many times, they simply show it as a R across the coil because
it's in series with a cap.

http://en.wikipedia.org/wiki/Snubber
 
In article <0001HW.D066606206DB1E51B05399BF@news.eternal-september.org>,
invalid@invalid.net says...
I have a 12V SPST cube relay in my junque box. The diagram molded into the
relayšs housing includes a component connected in parallel with the coil
which looks suspiciously like a resistor.

Itšs not a back-emf diode: I connected the relay coil using both polarities
(using a current-limited power supply) and the same current draw is measured.


What is the purpose of this resistor?

Thanks,
Dave
Click to expand...

Also, it could be a bidirectional TVS diode, those will clamp
either polarity when ever the voltage exceeds the coil rating.

Jamie
 
In article <MPG.2eab6a6c6cc7d5bc989ac2@news.eternal-september.org>,
"Maynard A. Philbrook Jr." <jamie_ka1lpa@charter.net> wrote:

In article <0001HW.D066606206DB1E51B05399BF@news.eternal-september.org>,
invalid@invalid.net says...

I have a 12V SPST cube relay in my junque box. The diagram molded into the
relay1s housing includes a component connected in parallel with the coil
which looks suspiciously like a resistor.

It1s not a back-emf diode: I connected the relay coil using both polarities
(using a current-limited power supply) and the same current draw is
measured.


What is the purpose of this resistor?

Thanks,
Dave

more than likely a snubber network, they normally have a
resistor and cap in a single component..

Many times, they simply show it as a R across the coil because
it's in series with a cap.

http://en.wikipedia.org/wiki/Snubber
Click to expand...

I haven't ever seen a snubber in a relay. It usually has the iron
designed to short-circuit fast field changes.

--
I will not see posts from astraweb, theremailer, dizum, or google
because they host Usenet flooders.
 
In article <mcmurtrie-0C54DC.19172817102014@news.sonic.net>,
mcmurtrie@pixelmemory.us says...
more than likely a snubber network, they normally have a
resistor and cap in a single component..

Many times, they simply show it as a R across the coil because
it's in series with a cap.

http://en.wikipedia.org/wiki/Snubber

I haven't ever seen a snubber in a relay. It usually has the iron
designed to short-circuit fast field changes.

--
Click to expand...

We buy 24VDC relays with snubber networks in side on the coil, it
removes the need to put one on the terminals. It comes in handy when
you're doing a few rows of relays with PLCs and micro controllers
involved. They don't like the little pulse noise in the lines.

Those with diodes in them are ok for driver component protection but
they still can generate a noise pulse, just not a damaging one.

When you have bundles of wires tightly packed together, in
race ways and wire harnesses, like in cars, it can cross talk very well.


Jamie
 
"Maynard A. Philbrook Jr." <jamie_ka1lpa@charter.net> wrote in message
news:MPG.2eab6a6c6cc7d5bc989ac2@news.eternal-september.org...
In article <0001HW.D066606206DB1E51B05399BF@news.eternal-september.org>,
invalid@invalid.net says...

I have a 12V SPST cube relay in my junque box. The diagram molded into
the
relayšs housing includes a component connected in parallel with the coil
which looks suspiciously like a resistor.

Itšs not a back-emf diode: I connected the relay coil using both
polarities
(using a current-limited power supply) and the same current draw is
measured.


What is the purpose of this resistor?

Thanks,
Dave

more than likely a snubber network, they normally have a
resistor and cap in a single component..

Many times, they simply show it as a R across the coil because
it's in series with a cap.
Click to expand...

Looking at a data sheet for an Omron automotive relay that shows this
'unknown device' across the coil, it appears to detail it in the specs as
"1.1k suppression". It gives the coil resistance with and without this
included. If there was any series C involved, then the coil resistance would
not change with or without the device. This leads me to believe that it is
nothing more or less than a simple current dumping resistor with a value of
1.1k

Arfa
http://en.wikipedia.org/wiki/Snubber
Click to expand...
 
On 10/17/2014 8:57 AM, DaveC wrote:
I have a 12V SPST cube relay in my junque box. The diagram molded into the
relayšs housing includes a component connected in parallel with the coil
which looks suspiciously like a resistor.

Itšs not a back-emf diode: I connected the relay coil using both polarities
(using a current-limited power supply) and the same current draw is measured.


What is the purpose of this resistor?

Thanks,
Dave




It's usually a suppression resistor. Bosch used them a lot.
Click to expand...
 
> It's usually a suppression resistor. Bosch used them a lot.

So the resistor dissipates the coil energy as the magnetic field collapses?
You still get back-emf; more than with a diode but less than without
anything?

This one is a Bosch.

Thanks.
 
On 10/19/2014 3:30 AM, DaveC wrote:
It's usually a suppression resistor. Bosch used them a lot.

So the resistor dissipates the coil energy as the magnetic field collapses?
You still get back-emf; more than with a diode but less than without
anything?

This one is a Bosch.

Thanks.

Pretty much.
Click to expand...
 
In article <ZTZ0w.212161$_r4.20675@fx25.iad>, tombiasi@optonline.net
says...
On 10/19/2014 3:30 AM, DaveC wrote:
It's usually a suppression resistor. Bosch used them a lot.

So the resistor dissipates the coil energy as the magnetic field collapses?
You still get back-emf; more than with a diode but less than without
anything?

This one is a Bosch.

Thanks.

Pretty much.
Click to expand...

:)
Jamie
 
"DaveC" <invalid@invalid.net> wrote in message
news:0001HW.D066606206DB1E51B05399BF@news.eternal-september.org...
I have a 12V SPST cube relay in my junque box. The diagram molded into the
relayšs housing includes a component connected in parallel with the coil
which looks suspiciously like a resistor.

Itšs not a back-emf diode: I connected the relay coil using both
polarities
(using a current-limited power supply) and the same current draw is
measured.


What is the purpose of this resistor?
Click to expand...

There are such things as bidirectional transient suppressor diodes.

Although I've never seen it on a car relay - a resistor isn't impossible, it
could act as a "Q-spoiler" to damp inductive ringing.

Or a bit more likely - a VDR.
 
On 10/24/2014 2:02 PM, Ian Field wrote:
"DaveC" <invalid@invalid.net> wrote in message
news:0001HW.D066606206DB1E51B05399BF@news.eternal-september.org...
I have a 12V SPST cube relay in my junque box. The diagram molded into
the
relayšs housing includes a component connected in parallel with the coil
which looks suspiciously like a resistor.

Itšs not a back-emf diode: I connected the relay coil using both
polarities
(using a current-limited power supply) and the same current draw is
measured.


What is the purpose of this resistor?

There are such things as bidirectional transient suppressor diodes.

Although I've never seen it on a car relay - a resistor isn't
impossible, it could act as a "Q-spoiler" to damp inductive ringing.

Or a bit more likely - a VDR.
Click to expand...

Think of it as an RC snubber without the C. The capacitance will be
whatever the coil and wiring supply.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
Think of it as an RC snubber without the C. The capacitance will be
whatever the coil and wiring supply.

Cheers

Phil Hobbs
Click to expand...

Don't you think that's starting to get a bit complicated Phil ? I would have
thought that the amount of C in the coil and associated wiring was
comparatively small - even given a car wiring loom. I reckon that its just a
simple damping load across the L to encourage it not to 'ring' so fiercely
as the field collapses ??

Arfa
 
On 10/25/2014 08:54 AM, Arfa Daily wrote:
Think of it as an RC snubber without the C. The capacitance will be
whatever the coil and wiring supply.

Cheers

Phil Hobbs


Don't you think that's starting to get a bit complicated Phil ? I would
have thought that the amount of C in the coil and associated wiring was
comparatively small - even given a car wiring loom. I reckon that its
just a simple damping load across the L to encourage it not to 'ring' so
fiercely as the field collapses ??

Arfa
Click to expand...

The reason you care about the ringing is primarily insulation
degradation due to the peak voltage. If the parallel resistor is six
times the coil resistance, the peak voltage kick will be close to six
times the drive voltage of the relay (because the coil current wants to
be constant).

That's how RC snubbers work, except that since they don't represent a DC
load, you can use lower value resistors (with a tradeoff in switching
speed, of course). The speed of the ringing is set mostly by the
capacitance of the winding, unless the snubber resistor is very small.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
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